A throng of rescue workers scoured the coastal Florida waters early Wedenesday morning looking for two people missing from an air ambulance crash. CNN's John Zarrella has the latest.

Authorities have already found the bodies of two others in the Atlantic Ocean, a U.S. Coast Guard spokesman said. The four passengers - two pilots, a doctor and a nurse - had just dropped off a patient at Fort Lauderdale-Hollywood International Airport and was headed back to Mexico, airport spokesman Greg Meyer said.

By early Wednesday, the debris field and search area for survivors had stretched to 20 square miles of the Atlantic, the Coast Guard said.

A distress call from one of the pilots came just moments after takeoff. An air traffic controller asked him to turn left and keep a certain altitude.

Coast Guard Petty Officer Mark Barney said the bodies of a man and woman were located just off the coast of Fort Lauderdale.

The two medical staff members worked for Air Evac International, said Albert Carson, the company's director of operations. The pilots worked for a chartered company. Carson said it was not immediately clear who was killed and who was still missing.

The investigation into the crash of Asiana Airlines Flight 214 continues with emerging details today, but it's likely to be many months before it becomes clear what caused the Boeing 777 to land in the runway.

The plane slammed into a runway at San Francisco International Airport, killing two and injuring dozens.

As Miguel Marquez reports, we now have a better sense of what happened seconds before the crash.

“At about 35 seconds out and 500 feet up the pilot told investigators he saw a bright light and in response looked at the controls in the cockpit, including the speed indicator,” Marquez reports.

According to the head of the NTSB, “At about 500 feet the airspeed was approximately 134 knots.”

“The 350 ton plane was already below the 137 knot speed to which the pilot believed he had set the auto throttle,” Marquez explains.

“And for the first time we are hearing that at nine seconds before impact, 100 feet above the ground one of the pilots expresses concern about the aircraft's speed.”

The NTSB says they are trying to determine who said that, a part of its commitment to put everything it can into finding out what caused this crash.

CNN is covering the latest from Asiana Airlines Flight 214's final moments in the air and the chaotic scene on the ground immediately after it crashed at San Francisco International Airport, killing two passengers.

Frightened witnesses and passengers on the plane made desperate calls for help moments after it crashed and burst into flames. This morning, we’re hearing their dramatic 911 calls.

“A chilling description of the traumatic scene as passengers escape the burning aircraft, and a desperate plea for emergency medical assistance,” Marquez explains.

The words on one call: "We've been down on the ground, I don't know, 20 minutes, a half-hour…There are people waiting on the tarmac with critical injuries, head injuries. We're almost losing a woman here…We're trying to keep her alive."

The investigation into the crash of Asiana Airlines Flight 214 continues with stunning new details this morning.

According to the head of the NTSB, of the three pilots in the cockpit at the time of the crash, the "flying pilot" was training on the Boeing 777 and the pilot "instructing" him was doing it for the first time.

The pilots tell investigators they had trouble with the "auto-throttle", a device that regulates speed. It was on and set to 137 knots, but seconds before the crash, the plane had slowed dangerously to 103 knots.

Asiana Airlines Flight 214 was flying far slower than recommended as it approached San Francisco International Airport just before its crash landing on Saturday, the head of the National Transportation Safety Board said Monday.

The Boeing 777 was traveling at approximately 106 knots (122 mph) upon impact and at about 118 knots (136 mph) 16 seconds before impact at an altitude of about 200 feet; the recommended speed upon approach to the runway threshold is 137 knots (157 mph), Deborah Hersman told reporters.

The onboard systems warned the crew the plane was about to stall four seconds before the crash, she said.

That warning comes in the form of a "stick-shaker," said Arthur Rosenberg, a pilot, engineer and partner with the New York-based law firm Soberman & Rosenberg, which specializes in litigation stemming from plane crashes. "It's basically saying, 'Hey idiot, wake up and do something ... Now!"